Telephone-circuit



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G. K. THOMPSON.

TELEPHONE CIRCUIT.

No. 595,004. Patented 1390.7,1897.

Sq Inventor UNrrnD STATES PATENT OFFICE.

GEORGE K. THOMPSON, OF MALDEN, MASSACHUSETTS, ASSIGNOR TO THE AMERICAN BELL TELEPHONE COMPANY, OF BOSTON, MASSACHUSETTS.

TELEPHONE-CIRCUIT.

SPECIFICATION forming part of Letters Patent No. 595,004, dated December '7, 1897. Application filed July 23,1897. Serial No. 645,720. (No model.)

To aZZ whom it may concern.-

Be it known that I, GEORGE K. THOMPSON, residing at Malden, in the county of Middle sex and State of Massachusetts, have invented certain Improvements in Telephone-Circuits, of which the following is a specification.

The present invention relates to metalliccircuit multiple switchboards in which the line and supervisory signals are automatically operated and the telephone-transmitters at the associated substations are energized from a centralized battery or source of current located at the central station.

The invention is associated with a form of substation-circuit which has been denominated a relay-circuit, for the reason that when a plug is inserted in a jack or socket of the circuit a relay operates to open the normal route of the circuit and thereby cut off the line signal and the signaling battery and leave the said signal on a severed branch. In such circuits it has been customary to employ a battery of high electromotive force for calling and talking, another battery of lower electromotive force for the test and for the supervisory signals, and a third battery of still lower power for the linesignals. By means of the present invention the circuits are so arranged and balanced that but one battery is employed for calling from the substation, for conversation purposes, for the operation of the supervisory signals, and to effect a satisfactory test.

The invention also consists in means for operating the supervisory lamp-signals Whereby less current is used in the signal-circuit and all contacts therein are avoided.

The invention is shown in the attached drawing, which represents two substations Y and Z, with telephone lines extending to spring-jacks and signal-controlling magnets in a telephone-switchboard. The switchboard is provided with a single pair of plugs and their plug-circuit, together with supervisory signals.

The telephones and signaling apparatus maybe of any well-known arrangement adapted for the operation of automatic signals, current in the line from a central source being determined by a switch at the substation operated in the use of the telephone. The line conductors 1 and 2 of the circuits L and L are led to contact-pieces 3 and 4 of spring-jacks J at the switchboard, after which the conductors terminate at the respective poles of the battery B by their extensions 1 an 2, the conductor 1 being grounded at G and the conductor 2 including in circuit the signal-controlling magnet 12, provided with an armature 13, which is connected by wire 7 to the extensions 2 of the conductor 2.

a is the supervisory lamp-signal in the circuit 14:, which terminates at one end in a contact 11 in proximity to the armature 13, its opposite end being grounded at G C is a cut-off relay, which may be of any suitable form, its electromagnet being, in a manner well known in the art, included in the test-circuit 6, which is grounded at G and provided with test-rings 5 at each spring-jack. The armature is shown as consisting of two arms 8 and 9, joined together by the insulating-block m and adapted to move as one piece. Their lower ends are permanently connected to the conductors l and 2, respectively, and their upper ends make electrical connection with contacts 1' and j of the said conductors.

P and P are the connecting-plugs, their tips I) connected by the wire 16, which includes the helices of the impedance and repeatin g coil N, and their sleeves c by the wire 17 ,which includes the helices of the impedance and repeating coil N and those of the electromagnets M and M whose armatures f control the passage of the light-rays of the super-' visory or disconnecting lamp-signals 6, located in the third wire 18 of the cord-circuit, which connects at one end with the plug-contact (Z and by its opposite end with the bridge 28 at the point 22. The repeating coils N and N are normally shunted by the wires 51 and 54:, respectively, and have sufficient electromagnetic resistance to prevent Voice-currents from the substations passing therethrough.v The bridge-wire 28 connects point 23 between the helices of the repeating coil N with point 27 between the helices of repeating coil N The common battery B is shown as located in the bridge 28 between the points 25 and 22, and a branch 21 extends from point 25 to ground G 20 represents an opaque non-conducting surface or partition, which in practice would be a strip upon the operators keyboards, in which is inserted small glass eyes or Windows 0, directly over the supervisory lamp-signals e. The armature f of the electromagnetic signal-controlling device M has an extension or shutter 15 at right angles thereto, which is adapted to be projected between the top of the lamp 6 and the under side of the eye 0.

30 is a bridge-wire including the operators telephones, adapted to be connected into the cord-circuit, and simultaneously therewith the shunts 51 and 54 are opened at their contacts and in a well-known manner.

In making a call the subscriber removes the telephone 25 from the hook-switch, which act closes the circuit at the contact p,whereupon current from battery B energizes the electromagnet 12, whose armature 13 engages contact 11, and a circuit is established from battery B, conductor 2 ,wire 7, armature 13, circuit 14, ground G2 and G and to battery through the line-signal a, which is lighted.

When the answering-plug P is inserted in the spring-jack J, its tip 2) makes contact with spring 8, its sleeve 0 with spring 4, and plate 01 with ring 5, and a talking-circuit is established from battery B through helix a: of coil -N ,wire 17, electromagnet lVLwhose armature f thereupon becomes attracted, contacts 0 and 4, and conductor 2 to substation Y, returning via conductor 1, 3, and 17, wire 16, and helix so of N to the opposite pole of the battery. At the same time a second circuit is established from battery B,wire 18, signal e, sleeve of plug d, wire 6 to ground G, and by ground G to the opposite pole of battery, resulting in the lighting of the lamp 6; but as the armature f is now attracted to the pole of the electromagnet M its shutter is interposed between the lamp and the glass window or eye 0 and the light-rays do not pass through the said eye 0. Consequently there is no signal indicated to theoperator.

By the completion of the latter or second circuit the electromagnet of relay 0 becomes energized and attracts the armatures 8 and 9, thereby opening the main circuit at contact-points 'i and j, whereupon the electromagnet 12 becomes demagnetized and its armature 13 falls back, opening the circuit 14 and extinguishing the line lamp-signal a.

When a test is to be made, the operatorstelephone set E is by any usual switch introduced into the circuit,which act also removes the shunts 51 and 54 from the respective repeating coils N and N and the tip of the plug P touched to the ring 5 of the circuit wanted. If the circuit is busy, a current will be circulating in the test-wire 6, as has been previously described, a portion of which will be diverted from the tip of the plug via wire 16, bridge-Wire 28, and wire 21, and to ground G and thence to ground G. Upon the removal of the tip from the ring a reactionary impulse or kick occurs through thebridge 30, which is heard in the telephone-receiver as a click, denoting that the circuit tested is engaged. If there be no current flowing in the wire 6, no click will be heard in the receiver.

If a connection is made by the plug P with a second substation-circuit Z, the sameeffects are produced in the right-hand side of the cord-circuit as described of the left side-t'. e., the supervisory lamp-signal e is lighted and its rays prevented from extending through the eye 0 by the interposition of the shutter of the electromagnet M and the flow of current from battery is produced in the main circuit and cut off from the line-signal extension by the relay 0 when the subscriber called removes the telephone.

When one or both of two connected substations hang up their telephone-receivers, the circuit is opened by the hook-switch, the current from the battery ceases to flow through theelectromagnets M, which are in the talking-circuit, and their armatures f fall back and permit the light-rays from the supervisory lamp-signal to pass through the windows 0 and become visible to the operator, who, understanding the light so displayed as an order to disconnect, withdraws the plugs from the spring-jacks, and the circuits resume their normal condition.

In the practical operation of the invention I have found it advisable to employ a battery of twenty-four volts, and if supervisory signals are used requiring a voltage as high as twenty volts the variation in the electromotive force of the battery will not be of sulficient importance to decrease the life of the lamp, whereas with a lamp of very much lower voltage the electromotive force must be kept almost constant or the lamp will be injured. By the use of a cut-off relay of about eighty ohms resistance the proper volume of test is maintained and a minimum current passes through the supervisory circuit.

I claim 1. The combination in a telephone system, of a number or group of substation-circuits, each extending to switch connections upon the switchboard-sections at a central station; a line-signal, and signal and circuit controlling devices for each circuit; with a switch: cord circuit having two main-circuit and one local-circuit conductors, a supervisory signal in the local-circuit conductor, an electromagnet controlling by a shutter or like device the display of said signal in one of the said main-circuit conductors, a bridge uniting the said three conductors, and a battery included therein, and provided with separate normal connections between its poles and the ends of the main conductors of the several substation-circuits, whereby the said battery is enabled to supply current for all of the several circuits and signals concerned, substantially as described.

2. The combination of a substation-circuit provided with spring-jacks at the switchboard-sections, and adapted for the operation of automatic signals, current in the line from a central source being determined by the telephone-switch at the substation, a line lampsignal, a controlling device therefor, and a circuit-controlling device and test-circuit, the conductors of said circuit terminating at the poles of a battery; with a cord-circuit comprising three conductors, a bridge between the conductors including said battery, and supervisory lamp-signals in one, and electromagnets for controlling the same in another of the said cord conductors, whereby upon the removal of the telephone from its switch at the substation, the line-signal is lighted; and upon the insertion of the answering-plug the line-signal is extinguished, a test-circuit established, a supervisory signal lighted and its rays shielded, as set forth.

3. In a telephone-exchange system, the combination of a substation-circuit, having at the central station spring-jack switches at switchboard-sections, and at the substation a telephone-switch controlling its conductive continuity; with a plug-and-cord-connection circuit comprising two main conductors with the said battery bridged between them, and a third conductor in a local signal and testcircuit of said battery, a supervisory or dis connecting signal lamp contained in said local and test circuit, and adapted for illumination whenever the plug is in the springjacl: switch of any line; and a shutter or screen for said lamp-signal controlled by an electromagnet in one of said main cord conductors, the said magnet being arranged to operate the said screen, and conceal said lamp when the substation-telephone is in use, but to remove the same, and display the said lamp when the telephone is replaced, and its hook-switch thereby actuated to open the main circuit, substantially as described.

4. I11 a cord-circuit the combination of two plugs each provided with three contacts which are respectively connected with each other by separate conductors; a bridge between the said conductors including a battery, and repeating impedance-coils as set forth; supervisory lamp-signals in each side of the bridge in one of the conductors, and electromagnets in another of the conductors, provided with armatures controlling screens for the said lamps, the said lamps being in local circuits at the central station, and the said electromagnets being in the main circuit, when their respective plugs are inserted in line-switches or spring-jacks, substantially as set forth.

In testimony whereof I have signed my name to this specification, in the presence of two subscribing witnesses, this 15th day of July, 1897.

GEORGE K. THOMPSON. lVitnesses:

GEO. XVILLIS PIERCE, KATHARINE DURFEE. 

